Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Vehicles can be configured to operate in an autonomous mode in which the vehicle navigates through an environment with little or no input from a driver. Such autonomous vehicles can include one or more sensors that are configured to detect information about the environment in which the vehicle operates. The vehicle and its associated computer-implemented controller use the detected information to navigate through the environment. For example, if the sensor(s) detect that the vehicle is approaching an obstacle, as determined by the computer-implemented controller, the controller adjusts the vehicle's directional controls to cause the vehicle to navigate around the obstacle.
One such sensor is a light detection and ranging (LIDAR) device. A LIDAR actively estimates distances to environmental features while scanning through a scene to assemble a cloud of point positions indicative of the three-dimensional shape of the environmental scene. Individual points are measured by generating a laser pulse and detecting a returning pulse, if any, reflected from an environmental object, and determining the distance to the reflective object according to the time delay between the emitted pulse and the reception of the reflected pulse. The laser, or set of lasers, can be rapidly and repeatedly scanned across a scene to provide continuous real-time information on distances to reflective objects in the scene. Combining the measured distances and the orientation of the laser(s) while measuring each distance allows for associating a three-dimensional position with each returning pulse. A three-dimensional map of points of reflective features is generated based on the returning pulses for the entire scanning zone. The three-dimensional point map thereby indicates positions of reflective objects in the scanned scene.
A hyperspectral sensor is a spectral analysis tool that captures an image with detailed spectral information of the scene on a pixelated basis. Rather than representing an image with red, green, and blue color content information for each pixel, each pixel can include a power spectral density values for a series of wavelength ranges. For instance, a hyperspectral sensor may generate 320×460 pixel images, with sensitivity to a range of wavelengths spanning 1000 nm and a resolution of about 4 nm. The data generated from such an image can be considered a cube of data values, with 320 by 460 length and width (pixelated image size) and 250 height (1000 nm/4 nm). By providing spectral information for spatially distinct regions of an image, distinct materials can be identified according to their characteristic spectral transmission and/or reflection “fingerprints.”
Some hyperspectral imagers are scanned across a scene while simultaneously taking spectra for a line of pixels. For example, received light is passed through a slit to select a single “line” of a scene being imaged. The slit of light is passed through a diffraction grating, to redirect the light according to wavelength and the diffracted pattern is passed to an imaging focal plane, where a detector characterizes the spectral content at each spectral band. Sweeping the hyperspectral sensor across a scene transverse to the elongated direction of the slit allows for gradually developing a two-dimensional picture of a scene. In another example, a series of images of a scene is captured while an adjustable filter is incrementally adjusted between each image to select for each wavelength band of interest. Each image then provides the spectral content of a scene at the particular spectral band selected for.